Fourteen antibiotic suppressed Osborne Mendel female rats were divided into three groups. Four were immunized subcutaneously (SC) with 5 ug of K1-BSA three times at two week intervals. Four were immunized SC with 5 ug of Type I pilus and a final six with 5 ug of HIB-BSA (Haemophilus influenza type B antigen). One week after the second immunization the rats were mated. After the dams delivered, the pups were divided such that groups of pups recieved antibody via the placenta alone, colostrum alone or by both routes. When the pups were six days old they were infected with 10 to the eight - 10 to the nine CFU of E. coli KRS203. Two days later bacteraemia was confirmed by plating blood samples onto agar plates containing antibody to K-1. Anti K1, Pilus and HIB antibodies in pup sera, and dam sera and colostra were analyzed by ELISA. No clear correlation was evident between serum antibody to K1 and pilus in the pups and/or colostral IgA and IgG anti K1 and pilus in the dams and protection against bacteraemia.